1. Field of the Invention
The present invention relates to a color filter which is obtained by coloring a colored layer with an ink jet method and is suitable for a color liquid crystal display.
2. Description of the Related Art
Recently, with the development of the personal computers, in particular, the development of the portable personal computers, demand for liquid crystal displays, especially for color liquid crystal displays tends to be increased. Further, bigger liquid crystal displays are in demand. However, the color liquid displays are expensive; therefore, a request that the cost should be reduced has been increasing. In particular, a request that the cost of their color filters, which accounts for a high ratio in the total cost, should be reduced has been raised.
Such color filters, in general, comprise colored patterns of three primary colors of red (R), green (G) and blue (B) so that liquid crystals are operated as a shutter by switching on or off the electrodes each corresponding to the pixels of R, G and B. Thereby, color display can be provided according to light transmission to the each pixel of R, G and B.
The color filter producing method which has been hitherto performed is, for example, a dye method. In this dye method, a water-soluble polymer which is a material for dyeing is first produced on a glass substrate, patterned into a desired shape in a photolithographic step, and then the resultant pattern is immersed into a dyeing bath to yield a colored pattern. This is repeated three times, thereby forming color filter layers in R, G and B.
Another example of the producing method is a pigment dispersion method. In this method, a photosensitive resin layer wherein a pigment is dispersed is first formed on a substrate, and patterned to yield a mono-colored pattern. This step is further repeated three times, thereby forming color filter layers in R, G and B.
Different examples of the method include an electrode positing method, and a method of dispersing R, G and B pigments in thermosetting resins, respectively, performing printing for R, G and B three times, and then thermosetting the resins. However, according to the methods, in any case, the same step should be repeated for three times for coloring the three colors of R, G and B so that problems are involved in that the cost is increased or the yield is lowered due to the repetition of the steps.
In such methods in particular, when plural colored layers in red (R), green (G), blue (B) and so forth are formed on a transparent substrate wherein a light shielding part is formed, it is difficult to form the colored layers into even shapes on the entire surface of a color filter. As illustrated in FIGS. 4A to 4E, a color layer 4R for a first color is formed in the opening portions made in a transparent substrate 1, on which a light shielding part 2 is formed, by such as photolithography method, so as to cover the light shielding part 2 partially (FIG. 4A). Subsequently, a colored layer forming coating solution 14B, for second colored layer formation, is applied onto the transparent substrate 1 on which the colored layer 4R is formed (FIG. 4B), and then the applied solution in only target regions is cured to form a colored layer 4B (FIG. 4C). At the time of applying the colored layer forming coating solution 14B, in the vicinities of the regions where the colored layer 4R is formed, the film thickness of the colored layer forming coating solution 14B applied onto the vicinities becomes large since the colored layer 4R is already formed on the transparent base material 1. Accordingly, the film thickness of the colored layer 4R side of the colored layer 4B, which is formed by curing the colored layer forming coating solution 14B, becomes larger than the film thickness of the colored layer 4R. When a colored layer forming coating solution 14G, for third colored layer formation, is applied (FIG. 4D), the colored layers 4R and 4G are already formed adjacently to regions where the third colored layer is to be formed; therefore, the film thickness of the film of the colored layer forming coating solution 14G becomes large in the vicinities of the colored layers 4R and 4G. Thus, when the coating solution 14G is cured to form a colored layer 4G, the film thickness of the colored layer 4G becomes larger at both end portions thereof than those of the colored layers 4R and 4B (FIG. 4E). Consequently, color unevenness is generated between the individual pixels. Moreover, even the pixels in the same color have different film thicknesses in accordance with the positions of the pixels in the color filter; it is therefore difficult to attain even color display in the whole of the color filter.
In the meantime, the applicant has been investigating a method for producing a color filter, including the steps of using a property changeable pattern forming coating solution containing a photocatalyst and a material having a property changed by the action of a photocatalyst accompanied by energy radiation to form a photocatalyst containing layer, exposing the resultant in a pattern form to light, so as to form a pattern with the property changed, and then forming a colored layer by such as an ink jet method (Japanese Patent Application Laid-Open No. 2001-074928). According to this method, the property of the photocatalyst containing layer is used to make it possible to form a colored layer easily.
According to such a method also, however, as illustrated in FIG. 5B, the shapes of pieces of a colored layer 4 in pixels in the central portion of a color filter are different from the shapes of pieces of a colored layer 4′ in outer side pixels of the color filter in many cases, depending on, for example, conditions for drying the colored layer forming coating solution dropped by such as an ink jet method. As illustrated in FIG. 5A, at the time of applying the colored layer forming coating solution, in the regions near the outside of the color filter, the solvent in this coating solution volatilizes upwards and toward end portions of the color filter. Consequently, in the regions near the outside of the color filter, the solvent in the atmosphere is lower in saturation degree and volatilization thereof advances further than in the central portion of the color filter. For this reason, as the volatilization of the solvent advances, the colored layer forming coating solution moves to the outer side so that the colored layer 4 is solidified in the state that the colored layer 4 deforms so as to be inclined outside, as illustrated in FIG. 5B. As a result thereof, in the whole of the color filter, the shape of the colored layer 4 in the individual pixels is not even. Thus, when the color filter is used in a liquid crystal display, even color display cannot be attained in the whole thereof.